Nakao, U.S. Pat. No. 6,134,008, issued Oct. 17, 2000, discloses an aligner and patterning method using phase shift mask. Exposure light is split into first and second exposure light beams and first and second phase shift masks are irradiated with the first and second exposure light beams. In the first and second phase shift masks a plurality of light shielding portions and a plurality of strip-shaped transmission portions are located between the plurality of light shielding portions for alternatively inverting the phase of transmission exposure light. Transmitted in combined exposure light resulting from interference is directed onto a photoresist material. In the above-described configuration, the aligner uses a phase shift mask for forming a fine and dense contact hole pattern and a patterning method thereof.
Kemp, U.S. Pat. No. 5,308,741, issued May 3, 1994, discloses a lithographic method using double exposures, physical mask shifting, and light phase shifting to form masking features on a substrate masking layer. A first phase shift mask is placed in a first position adjacent the substrate. The substrate is covered by the masking layer. The masking layer is exposed to light, or an equivalent energy source, through the first mask to form a first plurality of unexposed regions of the masking layer. Either a second mask or the first mask is placed adjacent the substrate in a second position which is displaced from the first position in at least one direction. A second exposure is used to form a second plurality of unexposed regions of the masking layer. The first and second pluralities of unexposed regions have common unexposed regions which are used to form the masking features.
Ham, U.S. Pat. No. 5,573,634, issued Nov. 12, 1996, discloses a method of forming contact holes of a semiconductor device. The method includes forming an insulating film over a semiconductor substrate. Thereafter, a photoresist film is coated over the insulating film. The photoresist film is exposed to light using a first exposure mask having windows adapted to allow portions of the insulating film corresponding to a part of contact holes to be exposed to the light, the part of contact holes having contact holes arranged diagonally to each other. The photoresist film is secondarily exposed to the light using a second exposure mask having windows arranged diagonally to each other and not overlapping with those of the first exposure mask. The light exposed portions of the photoresist film are removed to form a photoresist film having a pattern for exposing portions of the insulating film respectively responding to the contact holes.
Shimizu, U.S. Pat. No. 5,432,044, issued Jul. 11, 1995, discloses a method of forming a pattern using a phase shifting mask. The method includes forming a pattern using a phase shift mask which comprises applying at least first and second exposures. At least one exposure is conducted using a phase shifting mask and at least the other exposure is conducted for compensating the amount of light at a phase shifting boundary of the phase shifting mask.
Nakao, U.S. Pat. No. 6,162,736, issued Dec. 19, 2000, discloses a process for fabricating a semiconductor integrated circuit utilizing an exposure method. The exposure method includes forming a plurality of interlayer conductive paths through a first resist pattern which in turn is formed by an exposure of a hole pattern mask. A plurality of conductive lines is formed, adjacent the layer of conductive paths, through a second resist pattern which in turn is formed by double exposure of a line pattern mask and the hole pattern mask. Each conductive line is positioned on at least one of the conductive paths.
Lin et al., U.S. Pat. No. 6,664,011, issued Dec. 16, 2003, discloses a method including hole printing by packing and unpacking using Alternating Phase-Shifting Mask. The method includes adding extra holes to a given pattern of contact holes on the surface of a first mask, thus densifying the pattern of holes on the first mask and therefore reducing the range of hole-diameter to hole separation ratio. The pattern of added holes is alternating in phase with the pattern of desired holes. The added holes are filled up using a second mask.
The present invention provides alternatives to the prior art.